Recently, as the performance of focus detection apparatuses has become higher, many focus detection apparatuses of a so-called multi-point focus detection-type have been proposed that can perform focus detection at many points in a finder. In a focus detection apparatus that performs multi-point focus detection using the principle of a phase difference AF, a method is used in which a pair of focus detection images corresponding to the respective focus detection points is obtained to perform a correlation calculation, and the amount of defocus is calculated from a phase difference therebetween.
In this sort of focus detection apparatus, the number of photoelectric conversion portions for obtaining focus detection images has increased as the number of focus detection points increases. Conversely, it is very difficult to completely eliminate manufacturing defects in these photoelectric conversion portions. Japanese Patent Laid-Open No. 5-56355 discloses a technique for reducing the influence of a defect by interpolating a defective photoelectric conversion signal from the nearby signals. Furthermore, Japanese Patent Laid-Open No. 2001-177756 discloses a technique for eliminating the influence of a defect by using, as a focus detection signal, a portion that contains no defect among closely arranged photoelectric conversion portions.
Generally, a focus detection apparatus is required to be precise at the time of in-focus operation. Here, “precision at the time of in-focus operation” refers to the degree of absence of a difference between an image plane (position having the highest spatial frequency) of an imaging optical system and an in-focus position obtained by the focus detection apparatus.
However, in the methods described in Japanese Patent Laid-Open Nos. 5-56355 and 2001-177756, since a defective pixel in one focus detection image of a pair of focus detection images is interpolated, the correlation with the other focus detection image is lost, and such influences occur in a correlation calculation using the pair of focus detection images. Thus, the precision at the time of in-focus operation may be lowered. In particular, such influences easily occur in the case where a defective pixel is positioned at a characteristic point in an object image, such as the contour of an object.